Structural body formed by friction stir welding

ABSTRACT

End portions of face plates  111  and  112  of a frame member  110  are connected by a rib  116 A. To protrusion chips  117   b   1  and  117   b   2  end portions of face plates  101  and  102  of another frame member  100  are overlapped. The corners between the rib  116 A and the rear faces of the face plates  111  and  112  are in the form of a convex circular arc  131  which protrudes into a hollow portion  119  of the frame member  110 . Both end portions of the circular arc  131   b   1  are connected to the rib  116 A and the face plates  111  and  112  by two smooth recessed circular arcs  132   b   1  and  133   b   1 . Accordingly, since a flow-out of metal does not occur from this portion, the cross-section can be small and a light weight structure can be obtained. A structural body formed of hollow frame members which are joined by friction stir welding provides a light weight structure.

[0001] This application is a Divisional application of application Ser.No. 09/332,009, filed Jun. 14, 1999.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a structural body and to ahollow extruded frame member used to form the structural body byfriction stir welding. The invention relates more particularly to anovel joint shape of a structural body formed by joining hollow extrudedframe members using friction stir welding.

[0003] The present invention relates to a structural body and hollowextruded frame members used in forming the structural body by frictionstir welding, and the invention relates particularly to structuralmembers suited to use, for example, as an aluminum alloy member of thetype used in a railway vehicle and in building construction.

[0004] As described in Japanese application patent laid open publicationNo. Hei. 9-309164 (EP 0797043 A2), a friction stir welding method is amethod in which, by rotating a round rod (referred to hereinafter as arotary body) which is inserted into a joint between hollow extrudedframe members to be joined and by moving the rotary body along a line ofthe joint between the frame members to be joined, the joint of the framemembers is exothermally heated and softened and the joint is elasticallyfluidized to form a solid weld.

[0005] The rotary body for carrying out the friction stir weldingcomprises a small diameter portion which is inserted in the joint and alarge diameter portion which is positioned outside the joint. The smalldiameter portion and the large diameter portion of the rotary body havethe same axis. A boundary face portion between the small diameterportion and the large diameter portion of the rotary body is inserted alittle into the joint. The welding according to the friction stirwelding method may be applied to an abutting portion of two framemembers or to an overlapping portion of the frame members.

[0006] As disclosed in the above-state publication, a protruding portionof a frame member is provided at the portion of the frame member to besubjected to welding. This protruding portion of the frame member comesinto contact with the rotary body, so that the protruding portion of theframe member is welded using the friction stir welding method. Asfurther disclosed in the publication, a protrusion chip is provided atthe portion of the frame member to be subjected to welding. Thisprotrusion chip protrudes from a rib of an end portion of one of thehollow extruded frame members to be subjected to welding toward theother hollow extruded frame member to which it is to be joined. On thisprotrusion chip a face plate of the other hollow extruded frame memberis overlapped.

[0007] Since friction stir welding is carried out by inserting a rotarybody serving as a joining tool into a joint between the hollow framemembers to be welded causing metal to be fluidized, a large force isexerted on the frame members during welding. Namely, a large force isrequired for inserting the rotary body into the joint between the framemembers to be welded, and so the frame members must be constructed toendure this large force. As a result, when the hollow extruded framemembers are joined, as described in the above-stated publication, metaleasily flows to a rear side of the joint. Therefore, it is necessary tomake the protruding portion of the hollow extruded frame members ratherlarge for supplementing the amount of metal which flows in the joint.Further, void holes occur easily in a joining bead of the frame members.

[0008] As one means for preventing the above-stated various defects, thethickness of the frame member to be subjected to welding is made largeat the joint portion, thereby the flow-out of metal from the framemembers can be prevented. For example, by giving a large circular arcshape to the corner between the face plate and the rib at the joiningportion of the frame member, the thickness of an outer portion of theframe member to be subjected to welding can be increased. Further, forexample, by making the diameter of the circular arc shape of the cornerbetween the protrusion chip and the rib of the frame member large, thethickness of the outer portion of the frame member to be subjected towelding can be increased.

[0009] The above stated circular arc shape of the frame member to besubjected to welding is recessed toward a side of the fact plate of theframe member. Accordingly, the cross sectional area of the frame memberto be subjected to welding becomes large, with the result that theweight of the frame member increases.

SUMMARY OF THE INVENTION

[0010] An object of the present invention is to provide a structuralbody wherein a light weight joint member or light weight joining portionof the structural body can be attained and to provide a hollow extrudedframe member wherein a light weight joint member or a light weightjoining portion of the hollow extruded frame member can be attained.

[0011] Another object of the present invention is to provide astructural body having a small cross-sectional area and a hollowextruded frame member having a small cross-sectional area which can beeasily and effectively welded using friction stir welding.

[0012] The above stated object can be attained by shaping the cornerbetween a rib at a vicinity of a joining portion and a face plate of ahollow extruded frame member or a corner between a protrusion chip and arib of the hollow extruded frame member in the form of a circular arcwhich protrudes outwardly from the corner at the center thereof, namelya circular arc which protrudes toward an inner hollow portion of thehollow extruded frame member.

[0013] According to the present invention, a structural body ischaracterized in that it is formed of a first member having twosubstantially parallel first face plates and plural first ribs forconnecting the two first face plates, and a second member having twosubstantially parallel second face plates and plural second ribs forconnecting the two second face plates, wherein the first member and thesecond member are joined by two joining beads, one of the two joiningbeads joins one of the two first face plates of the first member to oneof the two second face plates of the second member, the other of the twojoining beads joins the other of the two first face plates of the firstmember and the other of the two second face plates of the second member.In accordance with the present invention, a corner between the first ribof the first member in the vicinity of one of the two joining beads anda rear face of the one of the two first face plates of the first memberat a position of a first hollow portion of the first member is in theform of a first circular protruding arc which extends into the firsthollow portion of the first member.

[0014] According to the present invention, a structural body ischaracterized in that it is formed of a first member having twosubstantially parallel first face plates and plural first ribs forconnecting the two first face plates, and a second member having twosubstantially parallel second face plates and plural second ribs forconnecting the two second face plates, wherein the first member and thesecond member are joined by two joining beads, one of the two joiningbeads joins one of the two face plates of the first member to one of thetwo second face plates of the second member, the other of the twojoining beads joins the other of the two first face plates of the firstmember and the other of the two second face plates of the second member.In accordance with the present invention, the two joining beads arepositioned respectively at an intermediate portion between a first ribof the first member and a second rib of the second member in thevicinity of the joint, and one of the two second face plates of thesecond member overlaps a protrusion chip which protrudes from the firstrib in the vicinity of the one of the two joining beads toward thesecond member. Further, the corner between the first rib in the vicinityof the one of the two joining beads and a rear face of one of the firstface plates at a position of a hollow portion of the two first membersis in the form of a circular protruding arc which extends into thehollow portion of the first member, and a corner between the second ribin the vicinity of the one of the two joining beads and a rear face ofone of the two second face plates at a position of a hollow portion ofthe second member is in the form of a circular protruding arc whichextends into the hollow portion of the second member.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a partially enlarged longitudinal cross-sectional viewshowing a structural body having a joint subjected to friction stirwelding according to one embodiment of the present invention;

[0016]FIG. 2 is a partially enlarged longitudinal cross-sectional viewof a structural body which is comprised of two hollow extruded framemembers and using the joint configuration of the structural body shownin FIG. 1; and

[0017]FIG. 3 is a partially enlarged longitudinal cross-sectional viewshowing a structural body having a joint subjected to friction stirwelding according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0018] A structural body according to one embodiment of the presentinvention will be explained with reference to FIG. 1 and FIG. 2. Amember to be subjected to welding by using, for example, friction stirwelding is made of a metal material, for example, an aluminum alloyhollow extruded frame member. By joining frame members, a structuralbody, for example, a car body of a railway vehicle, can be manufactured.With the joining of plural frame members, a side body structure, a roofbody structure, an end body structure, and a floor body structure of thecar body of a railway vehicle, can be constructed.

[0019] In the case of the side body structure and the roof bodystructure of the car body of a railway vehicle, the length of the framemember for constituting the side body structure or the roof bodystructure is equal to the length of the car body of the railway vehicleat the most. The longitudinal direction of the frame member forconstituting the side body structure or the roof body structure isdirected in the longitudinal direction of the car body of the railwayvehicle.

[0020] A first hollow extruded frame member 100 for constituting thestructural body comprises two substantially parallel face plates 101 and102, plural ribs 103 and 106A for connecting the face plates 101 and102, and two outwardly protruding portions 104 a 1 and 104 a 2, whichprotrude in the thickness direction of the frame member 100 and formpart of the protrusion chips 117 a 1 and 117 a 2, which extend in thelongitudinal direction thereof A second hollow extruded frame member 110for constituting the structural body comprises two substantiallyparallel face plates 111 and 112, plural ribs 113 and 116A forconnecting the face plates 111 and 112, two outwardly protrudingportions 114 b 1 and 114 b 2 which protrude in the thickness directionof the frame member 110, and two protruding chips 117 b 1 and 117 b 2,which protrude in a longitudinal direction from the rib 116A a an endportion of the frame member 110.

[0021] The plural ribs 103 of the frame member 100 are provided alongthe width direction of the frame member 100. Each rib 103 of the framemember 100 is provided to incline relative to the face plates 101 and102. The rib 106A of the frame member 100 is an end rib and is providedorthogonal to the face plates 101 and 102. The reference numeral 109denotes a hollow portion of the frame member 100. The plural ribs 113 ofthe frame member 110 are provided along the width direction of the framemember 10. Each rib 113 of the frame member 110 is provided to inclinerelative to the face plates 111 and 112. The rib 116A of the framemember 110 is an end rib and is provided orthogonal to the face plates111 and 112. The reference numeral 119 denotes a hollow portion of theframe member 110.

[0022] The end portion of the frame member 100 has two vertical faces121 a 1 and 121 a 2, two sloping faces 122 a 1 and 122 a 2, a horizontalface 123 a 1 for connecting the vertical face 121 a 1 and the slopingface 122 a 1, and a horizontal face 123 a 2 for connecting the verticalface 121 a 2 and the sloping face 122 a 2. The vertical face 121 a 1 isprovided at the end of the face plate 101 of the frame member 100, andthe vertical face 121 a 2 is provided at the end of the face plate 102of the frame member 100. The horizontal face 123 a 1 is provided inparallel with the face plate 101 of the frame member 100, and thehorizontal face 123 a 2 is provided in parallel with the face plate 102of the frame member 110.

[0023] The sloping face 122 a 1 of the frame member 100 is provided onthe inwardly facing side of the protrusion chip 117 a 1, and the slopingface 122 a 2 of the frame member 100 is provided on the inwardly facingside of the protrusion chip 117 a 2. The sloping face 122 a 1 of theframe member 100 is provided to form one side of an opening whichreceives the protrusion chip 117 b 1 of the frame member 110. Thesloping face 122 a 2 of the frame member 100 is provided to form theother side of the opening which receives the protrusion chip 117 b 2 ofthe frame member 110. The sloping face 122 a 1 is angled outwardly inthe thickness direction of the frame member 100 and joins an inward endof the horizontal face 123 a 1. The sloping face 122 a 2 is angledoutwardly in the thickness direction of the frame member 100 and joinsan inward end of the horizontal face 123 a 2.

[0024] The protruding portion 104 a 1 protrudes outwardly from the sideof the frame member 100 in the width direction of the frame member 100.The protruding portion 104 a 2 protrudes outwardly from the side of theframe member 100 in the width direction of the frame member 100. Theprotrusion chip 117 a 1 is provided at the end portion of the face plate101 of the frame member 100, and the protrusion chip 117 a 2 is providedat the end portion of the face plate 102 of the frame member 100.

[0025] The end portion of the frame member 110 has two vertical faces121 b 1 and 121 b 2, two sloping faces 122 b 1 and 122 b 2, a horizontalface 123 b 1 for connecting the vertical face 121 b 1 and the slopingface 122 b 1, and a horizontal face 123 b 2 for connecting the verticalface 121 b 2 and the sloping face 122 b 2. The vertical face 121 b 1 isprovided at the end of the face plate 111 of the frame member 100, andthe vertical face 121 b 2 is provided at the end of the face plate 112of the frame member 110. The horizontal face 123 b 1 is provided inparallel with the face plate 111 of the frame member 110, and thehorizontal face 123 b 2 is provided in parallel with the face plate 112of the frame member 110.

[0026] The sloping face 122 b 1 of the frame member 110 is provided onthe outwardly facing side of the protrusion chip 117 b 1, and thesloping face 122 b 2 of the frame member 110 is provided on theoutwardly facing side of the protrusion chip 117 b 2.

[0027] The sloping face 122 b 1 of the frame member 110 is provided toform an engaging portion which mates with sloping face 122 a 1 of theprotrusion chip 117 a 1 of the frame member 100, and the sloping face122 b 2 of the frame member 110 is provided to form an engaging portionwhich mates with the sloping face 122 a 2 of the protrusion chip 117 a 2of the frame member 100. The sloping face 122 b 1 is angled inwardly inthe thickness direction of the frame member 110 from an outward end ofthe horizontal face 123 b 1, and the sloping face 122 b 2 is angledinwardly in the thickness direction of the frame member 110 from anoutward end of the horizontal face 123 b 2.

[0028] The protruding portion 114 b 1 protrudes outwardly from the sideof the frame member 110 in the width direction of the frame member 110.The protruding portion 114 b 2 protrudes outwardly from the side of theframe member 110 in the width direction of the frame member 110. Theprotrusion chip 117 b 1 is provided at the end portion of the face plate111 of the frame member 110. The protrusion chip 117 b 2 is provided atthe end portion of the face plate 112 of the frame member 110.

[0029] The rib 116A of the frame member 110 is positioned on anextension line of a welding joint of the two frame members 100 and 110.More particularly, the face plates 111 and 112 of the frame member 110are supported by the rib 116A, which is positioned such that the axis ofa rotary body 20 to be used for the welding is positioned on anextension line of a center of the plate thickness of the rib 116A of theframe member 110. Both the vertical face 121 b 1 and the vertical face121 b 2 of the frame member 110 are positioned a little on one side ofthe center toward the frame member 110 from the center extension line ofthe plate thickness of the rib 116A. Both the vertical face 121 b 1 ofthe frame member 100 and the vertical face 121 b 2 of the frame member110 are provided within a range on the other side of the centerextension line of the rib 116A. The plate thickness of the rib 116A ofthe frame member 110 is greater than the plate thickness of the rib 106Aof the frame member 100.

[0030] When the two frame members 100 and 110 are abutted, the verticalface 121 a 1 of the frame member 100 and the vertical face 121 b 1 ofthe frame member 110 come into abutting contact with one another.Further, when the two frame members 100 and 110 are abutted, thevertical face 121 a 2 of the frame member 100 and the vertical face 121b 2 of the frame member 110 come into abutting contact with one another.However, this is an ideal case, and so, depending on the dimensiontolerance difference in the structural body, in many cases, a gap isformed between the vertical face 121 a 1 of the frame member 100 and thevertical face 121 b 1 of the frame member 110, and a gap also is formedbetween the vertical face 121 a 2 of the frame member 100 and thevertical face 121 a 2 of the frame member 110.

[0031] In FIG. 1 and FIG. 2, the sloping face 122 a 1 of the framemember 100 and the sloping face 122 b 1 of the frame member 110 areshown as being in contact with each other, and the sloping face 122 a 2of the frame member 100 and the sloping face 122 b 2 of the frame member110 are shown as being in contact with each other, but in many casesthere may be a gap between these faces.

[0032] When the two frame members 100 and 110 are assembled, thesurfaces of the outer faces of the two face plates 101 and 102 of theframe member 100 and the outer faces of the two face plates 111 and 112of the frame member 110 are joined. Namely, the sloping faces 122 a 1and 122 a 2 of the frame member 100 are recessed, but the sloping faces122 b 1 and 122 b 2 of the frame member 110 are raised. Accordingly, thetwo frame members 100 and 110 can be assembled easily.

[0033] In the middle of the corner between a rear face of the face plate111, which is positioned at the hollow portion 119 of the frame member110, and the rib 116A of the frame member 110 there is provided acircular arc portion 131 b 1 which protrudes into the hollow portion 119of the frame member 110, and a recessed circular arc portion 132 b 1 anda recessed circular arc portion 133 b 1 are provided on respective sidesof the circular arc portion 131 b 1. Further, in the middle of thecorner between a rear face of the face plate 112, which is positioned atthe hollow portion 119 of the frame member 110, and the rib 116A of theframe member 110 there is provided a circular arc portion 131 b 2, whichprotrudes into the hollow portion 119, and a recessed circular arcportion 132 b 2 and a recessed circular arc portion 133 b 2 are providedon respective sides of the circular arc portion 131 b 2. The recessedcircular arc portions 132 b 1 and 133 b 1 of the frame member 110 areproduced in the formation of the protruding circular arc portion 131 b 1of the frame member 110. The recessed circular arc portions 132 b 2 and133 b 2 of the frame member 110 are produced in the formation of theprotruding circular arc portion 131 b 2 of the frame member 110.

[0034] The recessed circular arc portions 132 b 1 and 133 b 2 of theframe member 110 are recessed from a tangent line which passes through acentral peak of the circular arc portion 131 b 1 of the frame member110. The protruding circular arc portion 131 b 1 of the frame member 110can be referred to as a circular arc shaped protruding portion inaccordance with the present invention. Also, the recessed circular arcportions 132 b 2 and 133 b 2 of the frame member 110 are recessed from atangent line which passes through a central peak of the circular arcportion 131 b 2 of the frame member 110. The protruding circular arcportion 131 b 2 of the frame member 110 can be referred to as a circulararc shaped protruding portion in accordance with the present invention.

[0035] The position of the circular arc portion 131 b 1 of the framemember 110 is determined to ensure that a predetermined distance R isprovided to a tip end of a small diameter portion 21 of the rotary body20 when the rotary body 20 is inserted to a predetermined position, asshown in FIG. 1. A center peak position of the circular arc portion 131b 1 of the frame member 110 is determined such that a position of acorner of the small diameter portion 21 of the rotary body 20, which hasbeen inserted to the above predetermined position, forms a standardbasis.

[0036] Since the insertion force of the rotary body 20 is supported bythe rib 116A of the frame member 110, in the prior art the metal canflow out easily to an outer portion from a surrounding portion of thisrib 116A. Accordingly, the thickness of the above-stated portionsurrounding this rib 116A of the frame member 110 is made larger.

[0037] According to experimentation performed by the inventors of thepresent invention, the distance from the corner of the small diameterportion 21 of the rotary body 20 to the peak of the circular arc portion131 b 1 of the frame member 110 is 5 mm, for example. In the prior art,the metal flows out easily through the gap formed between the slopingface 122 a 1 of the frame member 100 and the sloping face 122 b 1 of theframe member 110, and the metal also flows out easily through the gapformed between the protrusion chip 117 b 1 of the frame member 110 andthe rib 106A of the frame member 100. Herein, the dotted line in FIG. 1represents the shape of the corner between the rib and the face plateaccording to the conventional technique of the prior art. In thisexample of the prior art, the surface follows a linear line at a centralportion and has small circular arcs provided at both ends of the linearline. The linear line at the central portion is a tangent line whichcontacts a central portion of the circular arc 131 b 1 or the circulararc 131 b 2 of the frame member 110. As another example of the priorart, the entire connecting surface is formed to have a concave circulararc shape which is recessed toward a joining bead of the frame members100 and 110.

[0038] As will be understood from a comparison of the dotted line, whichdepicts the connecting surface according to the prior art, with thecontour of the connecting surface according to the present invention, across-sectional area of the parts, which comprise the portion betweenthe frame member 100 and the rib 106A and the portion between the framemember 110 and the rib 116A, can be made small by the employment of thepresent invention. As a result, according to this embodiment of thepresent invention, a frame member having a light weight structure forconstituting the structural body can be attained.

[0039] In this embodiment according to the present invention, therecessed portions are formed at both ends of the circular arc portion131 b 1 of the frame member 110 an also at both ends of the circular arcportion 131 b 2 of the frame member 110. However, it is possible toprovide such a recessed portion only at one end of the circular arcportion 131 b 1 of the frame member 110 or at only one end of thecircular arc portion 131 b 2 of the frame member 110. In such a case, ata side where the recessed portion is not provided, a linear line isconnected to an end portion of the circular arc, and this end portionand a rib (or a face plate) are connected by another circular arc. Inthis case, the weight of the structure of the frame member forconstituting the structure body also can be lowered.

[0040] A rear face at the tip end of the protrusion chip 117 b 1 of theframe member 110 is formed as a circular arc which grows thinner towardthe tip end of the protrusion chip 117 b 1 of the frame member 110.Also, a rear face at the tip end of the protrusion chip 117 b 2 of theframe member 110 is formed as a circular arc which grows thinner towardthe tip end of the protrusion chip 117 b 2 of the frame member 110. Theinner side of the protrusion chip 117 b 1 is formed as a circular arc135 b 1 and the inner side of the protrusion chip 117 b 2 is formed as acircular arc 135 b 2. The circular arc 135 b 1 has the same radius asthe circular arc 131 b 1 and the circular arc 135 b 2 has the sameradius as the circular arc 131 b 2.

[0041] The rotary body 20 for carrying out friction stir welding has asmall diameter portion 21 at a tip end of a large diameter round rodportion 20 a. A boundary face 20 b, formed between the large diameterportion 20 a and the small diameter portion 21 of the rotary body 20,has a circular shape which is recessed to a side of the large diameterportion 20 a. The small diameter portion 21 of the rotary body 20 is ascrew member.

[0042] The friction stir welding for joining the two frame members 100and 110 is carried out by rotating the rotary body 20 and inserting therotary body 20 into the joint between the two frame members 100 and 110and moving it along the line of the joint between the two frame members100 and 110. The axis of the rotary body 20 is tilted such that the sideof the large diameter portion 20 a of the rotary body 20 is inclinedagainst the moving direction of the rotary body 20 along the joint line.Accordingly, a rear end of the boundary face portion 20 b of the rotarybody 20 is inserted into the two frame members 100 and 110, however afront end of the boundary face portion 20 b of the rotary body 20 ispositioned outside of the outer face (in FIG. 1, in the case of theupper side protruding portion 104 a 1 of the frame member 100 and theupper side protruding portion 114 b 1 of the frame member 110) of anupper portion of an apex of the protruding portion 104 a 1 of the framemember 100 and an upper portion of an apex of the protruding portion 114b 1 of the frame member 110.

[0043] The rear end of the boundary face portion 20 b of the rotary body20 is positioned between the protruding portion 104 a 1 of the framemember 100 and the protruding portion 114 b 1 of the frame member 10 andthe outer faces of the two face plates 101 and 102 of the frame member100 and the two face plates 111 and 112 of the frame member 110. Theterm “rear end” and the term “front end” in this description of thepresent invention are defined in relation to the moving direction of therotary body 20 as a standard basis.

[0044]FIG. 1 shows a condition where the rotary body 20 is inserted to apredetermined depth into the two frame members 100 and 110 for formingthe structural body. In FIG. 1, a part of the tip end of the smalldiameter portion 21 of the rotary body 20 is omitted. The tip end of thesmall diameter portion 21 of the rotary body 20 is positioned in thevicinity of the horizontal face 123 a 1 of the frame member 100 and thehorizontal face 123 b 1 of the two frame member 110.

[0045] During the friction stir welding process, the two frame members100 and 110 are pressed together and are secured to a bed (not shown inthe figure) by means of a vise (not shown in the figure). To bring thesloping face 122 a 1 of the frame member 100 and the sloping face 122 b1 of the frame member 110 into firm contact with each other, the framemember 100 is pressed against the opposed frame member 110.

[0046] During the friction stir welding process, there is a roller (notshown in figure) which moves in accompaniment with the linear movementof the friction stir welding rotary body 20. The roller presses down onthe right and the left sides of the protruding portion 104 a 1 of theframe member 100 and on the right and left sides of the protrudingportion 114 b 1 of the frame member 110, on the upper portion of theprotruding portion 104 a 1 of the frame member 100 and on the upperportion of the protruding 114 b 1 of the frame member 110.

[0047] Each of the friction stir welding operations for joining theupper and lower portions of the frame member 100 and the frame member110 is carried out as follows. Namely, after one side of the two framemembers 100 and 110 has been joined by friction stir welding, the twoframe members 100 and 110 are turned over to perform friction stirwelding on the other side, or by providing two rotary bodies 20, asimultaneous friction stir welding can be carried out on both sides.

[0048] The number of the frame members 110 which are mounted on the bedis two or more than two. After the friction stir welding process, thestructural body obtained by this friction stir welding process iscarried out again to join a further frame member, until a structuralmember of sufficient length for the car body of the railway vehicle isobtained.

[0049] Since abutted faces of the frame members 100 and 110 are providedwith the sloping faces 122 a 1 and 122 a 2 on the frame member 100 andthe sloping faces 122 b 1 and 122 b 2 on the frame member 110, the twoframe members 100 and 110 can be assembled in such a way that slip-offin the up and down directions between the two frame members 100 and 110can be prevented.

[0050] Further, when the sloping face 122 a 1 of the frame member 100and the sloping face 122 b 1 of the frame member 110 and the slopingface 122 a 2 of the frame member 100 and the sloping face 122 b 2 of theframe member 110 are in contact with each other, in comparison with anon-contact condition, the flow-out of the metal from these portions asdescribed in the above-stated case can be prevented.

[0051] The gap formed between the vertical face 121 a 1 of the framemember 100 and the vertical face 121 b 1 of the frame member 110 isclosed, and a gap formed between the vertical face 121 a 2 of the framemember 100 and the vertical face 121 b 2 of the frame member 110 isclosed, by the flow of metal from the protruding portions 104 a 1 and104 a 2 of the frame member 100 and the protruding portions 114 b 1 and114 b 2 of the frame member 110.

[0052] The vertical faces 121 a 1 and 121 a 2 of the frame member 100and the vertical faces 121 b 1 and 121 b 2 of the frame member 110 mayhave a slight incline, however, it is necessary to move a large amountof metal from the protruding portions 104 a 1 and 104 a 2 of the framemember 100 and the protruding portions 114 b 1 and 114 b 2 of the framemember 110.

[0053] At the end portions of the protrusion chips 117 b 1 and 117 b 2of the frame member 110, the two sloping faces 122 a 1 and 122 a 2 ofthe frame member 100 and the two sloping faces 122 b 1 and 122 b 2 ofthe frame member 110 are provided. However, it is possible to providefaces which are parallel with the face plates 101 and 102 of the framemember 100 and the face plates 111 and 112 of the frame member 110.

[0054] After the friction stir welding process, as may be required, theprotruding face 104 a 1 of the frame member 100 and the protruding face114 b 1 of the frame member 110 may be cut off to provide a smooth faceon the outer surface of the face plate 101 of the frame member 100 andthe face plate 111 of the frame member 110. Also, the protruding face104 a 2 of the frame member 100 and the protruding face 114 b 2 of theframe member 110 may be cut off to provide a smooth face on the outersurface of the face plate 102 of the frame member 100 and the face plate112 of the frame member 110.

[0055] In a case where the structural member is employed as a car bodyof a railway vehicle, as shown in FIG. 2, the protruding face 104 a 1 ofthe frame member 100 and the protruding face 104 b 1 of the frame member110 are cut off or otherwise removed from the outer surface of the carbody of the railway vehicle. Also the protruding face 104 a 2 of theframe member 100 and the protruding face 104 b 2 of the frame member 110are cut off or otherwise removed from the outer surface of the car bodyof the railway vehicle. Reference numeral 30 a and 30 b shown in FIG. 2denote a joining bead of the two frame members 100 and 110,respectively.

[0056] A structural body and a hollow extruded frame member according toanother embodiment of the present invention will be explained withreference to FIG. 3. FIG. 3 is a partially enlarged longitudinalcross-sectional view showing a structural body having a joint member forapplication of friction stir welding according to the present invention.

[0057] In the structural body shown in FIG. 3, a welding joint ispositioned on a line which passes midway between a rib 106B of the framemember 100 and a rib 116B of the frame member 110. The corner betweenthe rib 116B and the face plate 111 of the frame member 110 is formed asone circular arc shaped protrusion 131 b 1, and the corner between therib 116B and the face plate 112 of the frame member 110 is formed asanother circular arc shaped protrusion chip 131 b 2.

[0058] A root of the rib 116B and the protrusion chip 117 b 1 of theframe member 110 are connected by a convex circular arc shaped portion141 b 1, which is raised to extend away from the face plate 111 of theframe member 110, and two concave circular arc shaped portions 142 b 1and 143 b 1, which are recessed toward the face plate 111 of the framemember 110. A root of the rib 116B and the protrusion chip 117 b 2 ofthe frame member 110 are connected by a convex circular arc shapedportion 141 b 2, which is raised to extend away from the face plate 112of the frame member 110, and two concave circular arc shaped portions142 b 2 and 143 b 2, which are recessed toward the face plate 112 of theframe member 110.

[0059] The corner between the rib 106B and the face plate 101 of theframe member 100 is formed as a convex circular arc portion 145 a 1,which is raised toward the hollow portion 109, and two concave circulararc portions 146 a 1 and 147 a 1, which are recessed toward the verticalface 121 a 1 of the face plate 101 of the frame member 100. Further, thecorner between the rib 106B and the face plate 102 of the frame member100 is formed as a convex circular arc portion 145 a 2, which is raisedtoward the hollow portion 109, and the two concave circular arc portions146 a 2 and 147 a 2, which are recessed toward the vertical face 121 a 2of the face plate 102 of the frame member 100.

[0060] The dotted line shown in FIG. 3 represents the shape of thecorner surface according to the conventional technique provided in theprior art, wherein the entire connecting surface according to theconventional technique forms a circular arc. The connection line in theform of a continuous circular arc according to the conventionaltechnique, which is in contrast to the circular arcs 141 b 1, 142 b 1and 143 b 1 of the protrusion chip 117 b 1, has been omitted. Also, theconnection line in the form of a continuous circular arc according tothe conventional technique, in contrast to the circular arcs 141 b 2,142 b 2 and 143 b 2 of the protrusion chip 117 b 2, has been omitted.Further, the two connection lines in the form of continuous circulararcs according to the conventional technique in the prior art at theside of the face plates 101 and 102 of the frame member 100 have beenomitted.

[0061] The dimensions of the circular arcs 131 b 1, 141 b 1 of the faceplate 111 of the frame member 110 and of the circular arc 145 a 1 of theface plate 101 of the frame member 100 are the same. Namely, the radiusof each of the circular arcs 131 b 1, 141 b 1 of the frame member 110and of the circular arc 145 a 1 of the frame member 100 has an equalsize. Further, the dimensions of each of the circular arcs 131 b 2 and141 b 2 of the face plate 112 of the frame member 110 and of thecircular arc 145 a 2 of the face plate 102 of the frame member 100 arethe same. Namely, the radius of each of the circular arcs 131 b 2 and141 b 2 of the frame member 110 and of the circular arc 145 a 2 of theframe member 100 has an equal size.

[0062] With the structural body and the hollow extruded frame member ofthis embodiment according to the present invention, since the loadduring the friction stir welding process is primarily supported by thetwo ribs 106B and 116B, the frame members in the vicinity of the tworibs 106B and 116B are formed to be thicker. The portions in thevicinity of the two ribs 106B and 116B are the connection parts of theface plates 101 and 102 of the frame member 100 and of the face plates111 and 112 of the frame member 110.

[0063] Further, with the structural body and the hollow extruded framemember according to this embodiment of the present invention, the totalvalue of the plate thicknesses of the two ribs 106B and 116B can be madesmaller than that of the structural body of the former embodimentaccording to the present invention as shown in FIG. 1 and FIG. 2. As aresult, with the structural body and the hollow extruded frame member ofthis embodiment according to the present invention, a light weightstructural body and a light weight hollow extruded frame member can beobtained.

[0064] While the plate thickness of the rib 116B of the frame member 110is made thicker than the plate thickness of the rib 116A of the framemember 100 shown in FIG. 1 and FIG. 2, the plate thickness of the rib106B of the frame member 110 and the plate thickness of the rib 116B ofthe frame member 110 can be the same thickness in this embodiment.

[0065] Further, each of the portions between the rib 106B and the faceplates 111 and 112 of the frame member 110, between the rib 106B and theprotrusion chip 117 b 1 of the frame member 110 and the protrusion chip117 b 2 of the frame member 110, and, further, each of the portionsbetween the rib 106B and the face plates 101 and 102 of the frame member100, are configured such that a light weight structural body and a lightweight hollow extruded frame member can be obtained.

[0066] Since the recessed portions 132 b 1 and 133 b 1 formed betweenthe concave circular arc portion 131 b 1 and the rib 116B of the faceplate 111 of the frame member 110 are small, and the recessed portions132 b 2 and 133 b 2 formed between the concave circular arc portion 131b 2 and the rib 116B of the face plate 112 of the frame member 110 aresmall, it is possible to employ a design in which no recessed portion isprovided in the frame member 110. For example, a tangent line isprovided between a peak end portion of the circular arc 131 b 1 and therib 116B, and this tangent line and the rib 116B are connected by acircular arc. When the protrusion chip 117 b 1 or 117 b 2 of the framemember 110 is provided at a side of the rib 106B, a similar effect canbe obtained.

[0067] Further, if the sloping face 122 a 1 of the face plate 101 of theframe member 100 and the sloping face 122 a 2 of the face plate 102 ofthe frame member 100 are omitted, a horizontal face can be employed. Inthis case, the sloping face 122 b 1 of the protrusion chip 117 b 1 ofthe frame member 110 and the sloping face 122 b 2 of the protrusion chip117 b 2 of the frame member 110 are omitted, and a horizontal face isemployed.

[0068] When the two frame members 100 and 110 are assembled, the slopingface 122 a 1 of the face plate 101 of the frame member 100 and thesloping face 122 b 1 of the face plate 111 of the frame member 110 arein contact with each other and a gap is provided between the verticalface 121 a 1 of the face plate 101 of the frame member 100 and thevertical face 121 b 1 of the face plate 111 of the frame member 110.Further, when the two frame members 100 and 110 are assembled, thesloping face 122 a 2 of the face plate 102 of the frame member 100 andthe sloping face 122 b 2 of the face plate 112 of the frame member 110are in contact with each other and a gap is provided between thevertical face 121 a 2 of the face plate 101 of the frame member 100 andthe vertical face 121 b 2 of the face plate 112 of the frame member 110.For example, the interval between the recessed portion of the slopingfaces 122 a 1 and 122 a 2 of the frame member 100 is smaller than theinterval between the raised portion of the sloping faces 122 b 1 and 122b 2 of the frame member 110. As a result, with the structural body andthe hollow extruded frame member of this embodiment according to thepresent invention, the flow-out of the metal from the sloping face 122 a1 of the frame member 100 and the sloping face 122 b 1 of the framemember 110 can be prevented, and further the flow-out of the metal fromthe sloping face 122 a 2 of the frame member 100 and the sloping face122 b 2 of the frame member 110 can be prevented.

[0069] The technical range accorded to the present invention is notlimited to the terms used to describe the various embodiments herein orthe terms used in defining the means for solving the problems inherentin the prior art, but includes a range equivalents which would beapparent to the man of the ordinary technical field to which theinvention is directed.

[0070] Although, the present invention has been described andillustrated in detail, it is to be clearly understood that thedescription is presented by way of illustration and example, and it isnot to be taken by way of limitation. The spirit and scope of thepresent invention are limited only by the terms of the appended claims.

[0071] According to the present invention, in the case where frictionstir welding is employed, a structural body and the hollow extrudedframe member can be made as a light weight structure.

What is claimed is:
 1. A structural body, comprising: a first memberhaving two substantially parallel face plates and plural first ribsconnecting said two substantially parallel face plates; and a secondmember joined to said first member by a friction stir welding, wherein:a portion in which the friction stir welding has been carried out islocated in a vicinity of a connection portion between a rib, of saidplural first ribs, at an end portion of said first member and one faceplate of said first member; and a connection line between said one faceplate of a hollow portion side of said first member, in the vicinity ofsaid portion in which the friction stir welding has been carried out,and said rib is in a form of a circular arc which protrudes into saidhollow portion.
 2. A structural body according to claim 1 , wherein bothends of the protruded circular arc are dented to direct for said portionin which the friction stir welding is carried out.
 3. A structural bodyaccording to claim 1 , wherein said portion in which the friction stirwelding has been carried out is located in an abutted portion betweensaid first member and said second member by the friction stir welding.4. A structure body according to claim 1 , wherein said rib at said endportion is substantially orthogonal to said face plate.
 5. A structuralbody according to claim 1 , wherein: a protrusion chip, protruding fromsaid portion in which the friction stir welding is to be carried outtoward a rear face of said second member, is provided on said firstmember; said second member is overlapped with said protrusion chip; andsaid protrusion chip and said rib are connected by a circular arc whichprotrudes in a direction toward the other face plate of the twosubstantially parallel face plates.
 6. A structural body according toclaim 5 , wherein a lower end of said protruded circular arc of saidprotrusion chip is dented in a side of said end portion.